1. Field of the Invention
This invention relates to a method and an apparatus for etching a ruthenium film, and more particularly to a method and an apparatus for etching a ruthenium film that is useful for etching away an unnecessary ruthenium film formed on or adhering to the peripheral region, backside or other portions of a substrate, such as a semiconductor wafer.
2. Description of the Related Art
In recent years, metals of the platinum group or their oxides have become candidates for an electrode material for use in forming a capacitor, which utilizes a high dielectric or ferroelectric material, on a semiconductor substrate. Among these metals ruthenium, because of its good film-forming properties, is being progressively studied as a feasible material
A ruthenium film can be formed on a substrate generally by sputtering or CVD. In either method, a ruthenium film is formed onto the entire surface of a substrate, including the peripheral region. As a result, a ruthenium film is formed also in the peripheral region of the substrate and, in addition, the backside of the substrate is unavoidably contaminated with ruthenium.
The ruthenium film formed on or adhering to the peripheral region or backside of a substrate (i.e., the no-device-formed region of the substrate) is not only unnecessary, but can also cause cross-contamination during later transportation, storage and various processing steps of the substrate. Therefore, the performance of a dielectric material can be lowered. Accordingly, after performing some treatments during the film-forming process or to the formed ruthenium film, it is necessary to completely remove the unnecessary ruthenium film. Further, in the case of using ruthenium as an electrode material for forming a capacitor, a step for removing part of a ruthenium film formed on the interconnection formed region of a substrate is needed.
However, a technique has not been developed yet which can remove an unnecessary ruthenium film formed on or adhering to a substrate or the like by wet etching. This is partly because ruthenium is a very stable substance, and cannot be etched even with a metal-etching agent such as nitric acid and aqua regia.
The present invention has been made in view of the above situation in the related art. It is therefore an object of the present invention to provide a method and an apparatus for etching a ruthenium film which can sufficiently etch away an unnecessary ruthenium film formed on or adhering to the peripheral region, especially the no-device-formed region, backside or other portions of a substrate.
Thus, the present invention provides a method for etching a ruthenium film, comprising: etching a ruthenium film formed on a substrate with a chemical liquid having a pH of not less than 12 and an oxidation-reduction potential of not less than 300 mVvsSHE (i.e., 300 mV versus, or as compared to, the SHE, or Standard Hydrogen Electrode). It has been confirmed that the above method can sufficiently etch away a ruthenium film formed on a substrate by sputtering or CVD. In order to secure a practical level of etching rate, it is preferred to use a chemical liquid having a pH of not less than 13 and an oxidation-reduction potential of not less than 500 mVvsSHE. The pH of the chemical liquid is more preferably not less than 14 because when the pH is 13 or less, there is a likelihood of precipitation of insoluble ruthenium dioxide, which will cause particle contamination.
The chemical liquid can be maintained at a pH of not less than 12 by using ammonia, an organic alkali or an alkali hydroxide.
Further, the chemical liquid can be maintained at an oxidation-reduction potential of not less than 300 mVvsSHE by using, for example, a halide oxidant.
Either a strongly alkaline oxidant solution or a mixed solution of an alkali solution and an oxidant solution can be used as the chemical liquid. The strongly alkaline oxidant solution or the mixed solution may be supplied to a predetermined portion of a ruthenium film formed on a substrate so as to etch away the ruthenium film at the predetermined portion.
The strongly alkali oxidant solution may be a solution of a halogenated oxygen acid salt, such as hypochlorite, chlorite, or bromate.
The alkali solution may contain at least one of ammonia, tetramethylammonium hydroxide, and trimethylamine, and the oxidant solution may contain at least one of bromine, iodine, chlorine dioxide, and ozone.
It is possible to supply the alkali solution and the oxidant solution separately to a predetermined portion of a ruthenium film formed on a substrate, and mix both solutions in site, thereby etching away the ruthenium film at the portion where both solutions are mixed.
The present invention provides an apparatus for etching a ruthenium film, comprising: a substrate holder for holding and rotating a substrate; a center nozzle disposed above a central portion of the substrate held by the substrate holder for supplying ultrapure water to a surface of the substrate; and an edge nozzle disposed above the peripheral portion of the substrate held by the substrate holder for supplying a chemical liquid having a pH of not less than 12 and an oxidation-reduction potential of not less than 300 mVvsSHE to the surface of the substrate.
The present invention also provides an apparatus for etching a ruthenium film, comprising: a substrate holder for holding and rotating a substrate; a center nozzle disposed above a central portion of a substrate held by the substrate holder for supplying one of an alkali solution and an oxidant solution to a surface of the substrate; and an edge nozzle disposed above the peripheral portion of the substrate held by the substrate holder for supplying the other one of the alkali solution and the oxidant solution to the surface of the substrate. A mixture of the alkali solution and the oxidant solution has a pH of not less than 12 and an oxidation-reduction potential of 300 mVvsSHE.
The present invention also provides an apparatus for etching a ruthenium film, comprising: a substrate holder for holding and rotating a substrate; a rotatable chemical liquid applicator that can be brought into contact with a bevel region of the substrate held by the substrate holder; and a chemical liquid supply pipe for supplying a chemical liquid having a pH of not less than 12 and an oxidation-reduction potential of not less than 300 mVvsSHE to the chemical liquid applicator.
The present invention further provides an apparatus for etching a ruthenium film, comprising: a substrate holder for holding a front surface of a substrate in a non-contact manner and rotating the substrate; and a back nozzle disposed so as to be directed toward the central portion of a backside of the substrate held by the substrate holder. While flowing an inert gas along the front surface of the substrate, a chemical liquid having a pH of not less than 12 and an oxidation-reduction potential of not less than 300 mVvsSHE is supplied from the back nozzle to the backside of the substrate